Perfume raw materials (PRMs) have their own inherent volatility as determined in part by their molecular weight (i.e., size) and in part by the interaction with their surroundings (i.e., ability to hydrogen bond with other PRMs or solvents). The volatility of the PRMs can span a wide range and impact the evaporation rate and/or release of the fragrance components from a composition into headspace (and thus becoming olfactorily noticeable). For example, highly volatile PRMs (i.e., greater than about 0.1 Torr (>0.013 kPa) at 25° C.), which tend to smell citrusy, green, light and fresh, may be noticeable for only a few minutes after being applied to a substrate. Less volatile PRMs (i.e., between about 0.1 to about 0.003 Torr (0.013 to 0.00040 kPa) at 25° C.), characterised by floral or fruity notes, may be detectable for several hours. The least volatile PRMS (i.e., less than about 0.003 Torr (<0.00040 kPa) at 25° C.) are typically heavy florals, sweet, musky and woody, and can last for several days. Although it may be acceptable in some situations to have fragrances remain on the applied substrate for long periods (e.g., fabrics to be stored in cupboard for days or weeks before use), generally, this is not suitable for many fragrance compositions.
Typically, consumers will use a fragrance composition (e.g., fine fragrance, deodorant, body lotion, etc.) and then remove it from their skin after a period of 8 to 24 hours. Indeed, consumers may actually wish to use another, differently scented product, in a shorter time frame than in between showering/bathing. Currently, consumers are either forced to mix a new scent with an old scent, if the old one has not completely evaporated, or alternatively remove the old scent by washing it off their skin. This provides an unpredictable or undesirable scent experience for users. Moreover, even though the old scent can be removed by washing, it represents a significant waste of product as “unused” product (and its accompanying scent) is washed down the drain. In fact, some consumers view the premature removal of the old scented product as being both costly and environmentally unfriendly.
Further, the possible types of fragrance profiles or characters to date have been somewhat limited due to the volatility of the PRMs. If perfumers wanted to design a fragrance with PRMs that evaporate in a given time frame applicable for personal care applications (i.e., 1 to 12 hours after application), then they would be restricted to the highly volatile PRMs characters (e.g., citrusy, green, light and fresh). They would be unable to create fragrance profiles derived from the less or least volatile PRM characters (e.g., heavy florals, spicy, sweet and musky notes). Thus, it is advantageous to be able to create fragrance compositions that span a wider range of fragrance characters while still having all or substantially all of the PRMs evaporated within a given time frame (i.e., 1 to 12 hours after application).
Recently, ionic liquids have been used in the fragrance industry for dealing with solvent applications of the synthesis of fragrance materials or with the extractions of naturally derived PRMs (Sullivan, N., Innovations in Pharma. Tech. 2006, 20:75-77). For example, Forsyth et al. investigated the utilisation of ionic liquid solvents for the synthesis of lily-of-the-valley fragrance and fragrance intermediate Lilial (Forsyth et al., J. Mol. Cat. A. 2005, 231:61-66). Additionally, the utilisation of ionic liquids to suppress evaporation of fragrances in consumer products has also been gaining attention (Davey P., Perfumer Flavorist 2008, 33(4):34-35). For instance, ionic liquids have been used as “fixatives” with fragrance compositions to delay the rate of evaporation of the perfume component to impart increased stability/longevity of the fragrance (Petrat et al., US2006/0166856). Ionic liquids have also been used as pro-fragrances where PRM is appended covalently to either the cation or the anion (Rogers et al., US2012/046244; Blesic et al., RSC Advances, 2013, 3:329-333).
Accordingly, as discussed above, the prior art efforts have focussed only on delaying the evaporation of PRMs through the use of ionic liquids. As such, the prior art still has limitations, and does not adequately teach how to use ionic liquids in fragrance compositions for enhancing evaporation of PRMs. Therefore, there remains a need for a fragrance composition that comprises ionic liquids to control in a targeted manner, increases in the evaporation and/or release of PRMs from the fragrance composition. There is also a need for a fragrance composition that has a substantial proportion of the PRMs evaporated within a given time frame (i.e., 1 to 24 hours after application).